For LCDs it's a lot easier to figure out -- take the dimensions in each direction and divide by the number of pixels the laptop supports natively in that direction.
For example, my MAG LCD is a 19" diagonal, with 1280x1024 native resolution. It's 377mm wide x 300mm tall, so that yields a pitch of ~0.294 horizontal and ~0.293 vertical. If you can find a 17" LCD with the same native resolution, then it will obviously be better. AFAIK, 1280x1024 is standard for 19" screens (and pretty common for most 17" screens) so that is probably what you'll find. I can say, though, that with using a DVI connection on this monitor I can't tell pixels apart unless I get in really close and squint/stare at the screen, and I have good eyesight. If you're looking for something better than that, I can't personally think of any 17" or 19" LCD screens that have a 1600x1200 resolution, though most (if not all) 20" LCDs have that as their native resolution. FWIW, if you have a nice enough video card and are using a DVI connection, you probably will not be able to differentiate pixels on an LCD of any decent quality. No, I have no idea why laptop displays are so much higher resolution than desktop displays, and I wish it weren't so, but that's just the way it is.
HTH